Numerous interconnection applications exist which currently utilize cumbersome soldering operations. In order to render the high volume manufacturing processes more efficient, as well as reducing part count and cost, an alternative packaging technique is desirable. Toward this goal, inherently conducting polymers such as polyanilines, polythiophenes, polyparaphenylenevinylenes, polypyrroles, etc., have emerged as a new and reliable class of materials for use in a broad range of electronic packaging applications.
Conducting polymers can be conveniently employed in applications where the use of metal would be too expensive or inappropriate due to processing considerations. Such applications generally require that the physical properties of the interconnect material impart resiliency, high initial and ultimate adhesion as well as corrosion resistance and especially flexibility. The combination of such properties is difficult to achieve with an all metal connection.
Presently one class of interconnect technology, pressure sensitive adhesives are made by dispersing conductive fillers, such as metal-coated graphite fibers or flakes, metal spheres and/or flakes, particles, fibers, or carbon in an electrically insulating polymeric binder or carrier. There are a number of problems associated with this technology. These include high filler costs, sloughing of the filler, physical property degradation through environmental stress cycling and low surface conductivity. In addition, the loading of the filler in these systems often exceeds 50% by volume. At such high loading levels, the physical properties of the adhesive degrades. To circumvent these problems, the use of electrically conducting polymers in pressure sensitive adhesive formulations has been developed in accordance with the present invention to result in pressure sensitive adhesives which: (1) have good physical and mechanical properties including good tack, adhesion, cohesive strength and flexibility; (2) have high surface conductivity at reasonable loading levels; (3) do not slough; (4) are corrosion resistant.
Electrically conducting organic polymers have been of scientific and technological interest since the late 1970's. These relatively new materials exhibit the electronic and magnetic properties characteristic of metals while retaining the physical and mechanical properties associated with conventional organic polymers. Technological application of these polymers are beginning to emerge. These polymers are electrically conductive substituted and unsubstituted polyanilines, substituted and unsubstituted polyparaphenylenes, substituted and unsubstituted polyparaphenylenevinylenes, substituted and unsubstituted polythiophenes, substituted and unsubstituted polyazines, substituted and unsubstituted polyfuranes, substituted and unsubstituted polypyrroles, substituted and unsubstituted polyselenophenes, substituted and unsubstituted polyphenylene sulfides and substituted and unsubstituted polyacetylenes formed from soluble precursors. Blends of these aforementioned polymers are suitable for use as are copolymers made from the monomers used to form these polymers.
The articles entitled Polyaniline; Processability From Aqueous Solutions and Effective Water Vapor on Conductivity to M. Angelopoulos et al., Synthetic Metals, 21 (1987) pp.21-30, and the article entitled Polyaniline: Solutions, Films, and Oxidation State to M. Angelopoulos et al., Mol. Cryst. Liq. Cryst. 160-151 (1988), describe a chemically synthesized emeraldine base form of polyaniline which is soluble in various solvents. The emeraldine base is doped by reacting, the emeraldine powder or film with aqueous acid solution for several hours, for example, aqueous acetic acid or aqueous HCl.
U.S. Pat. No. 3,907,557 discloses electrostatic imaging labels consisting of an electrostatic face material which is an photoconductor, a non-conducting adhesive layer, and a release liner coated with an ionic conducting agent.
U.S. Pat. No. 4,842,768 discloses a conducting adhesive consisting of a polymerizable ionic unsaturated monomer, a silyl methacrylate monomer and a methacrylate monomer in water.
U.S. Pat. No. 4,855,077 discloses an ionic conducting sticking agent attained by adding an ionic conductor to the reaction product of a polyurethane/alcohol prepolymer and a polyurethane/isocyanate prepolymer.
U.S. Pat. No. 4,830,776 discloses a conducting pressure sensitive adhesive consisting of an adhesive isobutylene polymer and a conducting quaternary ammonium polymer.
U.S. Pat. Nos. 4,539,996 and 4,524,087 disclose a biomedical electrode and a process for forming same by coating an adhesive onto a conducting electrode. The references disclose adhesives cited in the prior art which were made conductive by addition of ionic monomers.
U.S. Pat. No. 4,554,924 discloses an improvement to U.S. Pat. Nos. 4,539,996 and 4,524,087 wherein ionic salts are added to the adhesive formulation to form non-polarizing biomedical electrodes.
U.S. Pat. No. 4,273,135 discloses a disposable biomedical electrode containing a hydrophilic polymer between the electrode surface and the skin.
U.S. Pat. No. 4,848,353 discloses a composition of a conducting pressure sensitive adhesive consisting of a polymeric matrix obtained by the copolymerization of a hydrogen donating monomer such as acrylic acid and a hydrogen accepting monomer such as N-vinylpyrrolidinone. The matrix is mixed with a conducting plasticizing solution comprising a water solution of a salt and a glycerol compound.
In each of the references cited above there is no composition cited which discloses or implies the composition of the present invention.